I contacted TuneIn and got this reply...bummer :-(
Thanks for getting back to us. If you have not received our response, I’d be glad to re-send it.
At this time, Premium is not supported in the Tesla. The TuneIn Premium subscription service is currently only available on our website, tunein.com, and on our iOS, Windows 10, and Android apps. We do hope to expand our Premium offering to more platforms in the future.
In the meantime, the best way to listen to TuneIn Premium in your car is by downloading the app for your mobile device, and connecting to your infotainment system through an auxiliary cord or Bluetooth.
We appreciate your patience! And please feel free to reach out if you have any further questions or concerns.